Polycarbonates are engineering plastics having excellent impact resistance, heat resistance, and transparency and widely used as various types of mechanical parts, optical disks, and automobile parts. Recently, higher fluidity is required in the field of optical disks.
In response to this requirement, a polycarbonate which is obtained by interfacial polycondensation using a solvent such as methylene chloride and has a chain end structure modified with a group such as cumylphenoxy group has been proposed (Japanese Patent Application Laid-Open No. Heisei 1(1989)-245016). However, complete removal of impurities, such as sodium and chlorine, from the polycarbonate obtained by the interfacial polycondensation is difficult, and the polycarbonate is not satisfactory for optical applications.
On the other hand, as the process for obtaining a polycarbonate containing decreased amounts of impurities without using any solvent, a transesterification process (a melt polymerization process) is known. As the process for producing a polycarbonate having cumylphenoxy group at the chain ends in accordance with this transesterification process, for example, a process in which a catalyst comprising a combination of a basic compound containing nitrogen, an alkali metal compound or an alkaline earth metal compound, and boric acid is used as the polymerization catalyst (Japanese Patent Application Laid-Open No. Heisei 2(1990)-175723) and a process in which polymerization is conducted in the presence of an alkali metal compound or an alkaline earth metal compound used as the catalyst, and then an acidic compound is added (Japanese Patent Application Laid-Open No. Heisei 5(1993)-9287) have been proposed. However, polycarbonates obtained in accordance with these processes have a problem in that cracks are formed at high temperatures in high moisture and strength is decreased.